We propose to conduct an explanatory open study of cyclical intravenous pamidronate administration in children with moderate to severe OI to test the hypotheses that pamidronate will 1) significantly increase bone mass 2) reduce chronic bone pain 3) reduce the overall level of disability and 4) reduce disease activity assessed biochemically and histomorphometrically. The principal outcome measures to be assessed will be: 1) lumber spine and femoral neck bone mineral content and bone mineral density. 2) fracture rate and pain. 3) biochemical parameters of bone formation/resorption. 4) bone histomorphometry. 5) disability evaluation. 6) evidence of restoration of vertebral morphometry.